For petroleum products sold in the retail sector, the method currently used to calibrate meters is dangerous and outdated. In the Prior Art, for each meter, the technician performs the following steps:                1. Place the calibration tank on the ground;        2. Fill the calibration tank with the fuel nozzle of a gas pump;        3. Kneel and take the measurement of the level of the liquid;        4. Write the measurement down;        5. Empty the calibration tank making sure it is truly empty, for the next filling (the technician must not see any drops dripping down for a certain amount of time);        6. Adjust the calibration of the meter; and        7. Repeat steps 1 through 6 until the calibration is adequate.        
During the whole process, spills, fumes and damage are inevitable and the technician is constantly exposed to fumes. Accidents are frequent.
The main inconvenience the need to wait until the last drops have fallen during the emptying of the tank.
U.S. Pat. No. 5,277,053 by Campbell describes a method by which calibration of current systems are done under actual conditions. It includes a first measure at a distance of a first spot, followed by a second measure from a second spot, knowing exactly the move from the first spot, that way the measures are done with a precise knowledge of the shift to get a constant calibration.